Rumor are rampant that the Federal Reserve will boost interest rates tomorrow. . . Dow Jones industrial average down 8.42 points, closing at 3,760.29 . . . N.Y.S.E.'s composite index down 0.25 to 254.52 . . . NASDAQ stock gained 1.28 to 732.89. . . American Stock Exchange down 0.38 to 443.32 . . . Gold rose $1.00 to $377.20 on the Commodity Exchange in New York . . . The 30-year Treasury bond closed with a yield of 7.50 percent, down from 7.49 late Friday.